(1) Field of the Invention
The present invention relates to a shock absorbing structure for a vehicle and an attachment structure for such a shock absorbing structure, and particularly relates to a shock absorbing structure for a vehicle that is intended to protect a pedestrian and a vehicle occupant by moderating a shock applied to the pedestrian or the vehicle occupant at the time of a contact with the pedestrian or objects other than the pedestrian, or at the time of a car crash, and to a structure for advantageously attaching such shock absorbing structure to the vehicle.
(2) Discussion of Related Art
Conventionally, in many vehicles, shock absorbing structures are provided on a vehicle mounted component, such as a pillar garnish, a roof side rail or an instrument panel which is highly possible to come into contact with the vehicle occupant's head or a leg at the time of the car crash, at a side of the vehicle mounted component opposite to the vehicle interior compartment (rear side). In this way, when the vehicle occupant comes into contact with the internal components at the time of the car crash etc., the shock to be applied to the vehicle occupant is moderated, hopefully protecting the occupant. Also, in recent years shock absorbing structures have been fitted not only to interior components but also to inner sides of external components such as a bumper etc., that have a high likelihood of coming into contact with a pedestrian when the pedestrian's leg, for example, contact with these external components while the vehicle is traveling, a collision energy generated accompanying the contact is absorbed by deformation of the shock absorbing structure, and it is also possible to take pedestrian protection measures that are intended to reduce a risk of an injury to the pedestrian's leg.
As is well known, there are many different types of the shock absorbing structure having various configurations, for example, as a shock absorbing structure fitted at an inner side of a bumper, there are (a) a structure formed from bent plates of a metal such as an aluminum or a steel presenting a cross sectional shape that resembles a U-shape, so that the shock absorbing structure is subjected to a buckling deformation when a shock is applied (for example, see JP-A-2003-285704 and JP-A-2004-322876); and (b) a structure formed of a resin foam body presenting a hollow shape (see, for example, to JP-A-2004-168077 and JP-A-2004-224106). Of these, with the shock absorbing structure (a), with respect to an initial stage of an application of the shock, a load applied to the structure suddenly increases with a small amount of displacement, and after that regardless of any increase in the amount of displacement the load value changes substantially constantly, and an ideal load displacement characteristic tracing a rectangular pulse is ensured. Also, with the shock absorbing structure of (b), compared with the shock absorbing structure of a conventional solid resin foam body, there are improved not only far better lightweight properties are obtained, but the shock absorbing characteristics at the initial stage of the application of the shock.
However, with the shock absorbing structure formed from the bent metal plate, not only the weight is significant, which has a detrimental effect on a fuel consumption, but also it is difficult to adapt overall a shape of the shock absorbing structure to the shape of an installation space since a moldability is poor. Also, with the shock absorbing structure formed with the hollow resin foam body, it is not possible to obtain the load displacement characteristic that displays a rectangular wave shape, and also, since a crack is easily occurred at the time of the application of the shock, it is not a simple matter to stably secure the shock absorbing characteristics that do not vary for each of the shock absorbing structures. Specifically, the shock absorbing structures of (a) and (b) described above have some inherent problems that need to be improved upon.
In the light of the situations as described above, there has been proposed (c) a shock absorbing structure for a vehicle consisting of a resin main body having a top wall to which an shock is applied, and side walls, for absorbing shock by being buckled and deformed by the application of the shock, provided integrally with the top wall so as to extend in the direction that the shock is applied, in a state positioned respectively opposite each other in pairs on a surface of the top wall opposite to the surface to which the shock is applied wherein a cross sectional shape of the main body parallel to a direction in which the shock is primarily applied is a U-shape (for example, see JP-A-2005-510393 and JP-A-2005-104164). With this type of the shock absorbing structure, by forming it from a resin molded body, an excellent moldability and lightweight properties are exhibited, and owing to an arrangement of absorbing the shock by a buckling deformation of the side wall, an ideal load displacement characteristic tracing the rectangular wave shape is ensured, and the problems associated with the shock absorbing structures of (a) and (b) described above are completely resolved.
However, with these types of shock absorbing structures of the related art, for example, depending on the size of the installation space, when the amount of an absorption of the collision energy is increased within a limited stroke, there is normally adopted a structure that raises a target load value of the load displacement characteristic within a permissible range. However, in an actual situation, it is difficult to increase the amount of the absorption of the collision energy as much as hoped for, by simply increasing a thickness of these types of side walls. On the contrary, there is caused an increase in a weight of the shock absorbing structure by increasing the thickness of the side wall. Specifically, with the shock absorbing structure of (c) described above, it is not easy to perform a tuning of the load displacement characteristic so that the amount of the absorption of the collision energy becomes a desired amount, and there is still room for improvement.